Responses
this reminds me of "extraordinary you" but it wasn't a manga and I don't see it on this site, maybe it goes by a different name but it's available on webtoon
So I searched extraordinary you and found the manhwa. Thank you(づ￣ ³￣)づ
https://www.mangago.zone/read-manga/july_found_by_chance/
So the fl was a side character of a high school manga. She had weak heart and is supposed to die in the story. Also, she has a bf or fiance who doesn’t love her. She gains awareness in the manga and wants to change her fate by altering the story. She starts dating a very insignificant male character in the manga who was very sweet. But as he's not an important character and fl is just a side character, they can hardly meet so dating was difficult.
I don't remember the ending but the whole thing felt like a fever dream.